tickling is a common, perhaps universal, human experience. Depictions of people engaged in some kind of tickling activity, whether between siblings, parents and children, or lovers, can be found in the art of many countries and cultures. Tickling someone often causes them to smile and laugh in a way that is indistinguishable from the reaction to other forms of pleasure or even intense amusement. However, tickling is a curious, paradoxical phenomenon. Particularly ‘ticklish’ individuals wriggle and writhe in apparent agony, as well as laughing hysterically, when being tickled. Francis Bacon in 1677 commented that: ‘[when tickled] men even in a grieved state of mind … cannot sometimes forbear laughing.’

Tickling usually occurs only between people who know each other well: children are likely to be tickled by their parents and siblings, adults may be tickled by their lovers. Normally the tickler is someone who desires to express intimacy, emotion, and affection through their tickling — in other words the tickle is intended as a friendly gesture. The degree of ‘ticklishness’ increases if the ‘ticklee’ feels that he or she cannot escape from the tickler. Although there is often such inequality of power during tickling, it normally occurs in situations that are entirely non-threatening. Charles Darwin in 1872 claimed that if a stranger tried to tickle a child the child would scream with fear rather than squeal with laughter.

But tickling is a pleasure that ‘cannot be reproduced in the absence of another’ as Adam Phillips wrote. The inability to tickle oneself seems to be hard-wired in the central nervous system: the brain reacts differently when people tickle themselves compared with when someone else does the tickling. The areas of the cerebral cortex associated with the sensation of touch (the somatosensory cortex) and pleasure (the anterior cingulate cortex) react much more strongly to a tickling stimulus delivered by an external agent than to a self-tickle. This hard-wired mechanism suggests that tickling is useful in social bonding — there is little point in social bonding with oneself.

This view was argued by Charles Darwin over a century ago. He wrote that tickling is an important aspect of social and sexual bond-ing, and prominent in the development of communication between mothers and babies. Tickle-induced laughter, he argued, is socially stimulated and results from close physical contact with another person. An alternative claim is that the laughter is purely reflexive — something that happens without our voluntary control, similar to the reflex muscle contraction induced when a doctor taps the tendon of your knee. Just as people laugh when they read an amusing story on their own, so they will laugh out loud when they are being tickled by a robotic hand, even when no other person is around to hear them.

Some animals seem to be ticklish. Great apes (chimpanzees and gorillas) react with what is believed to be an analog of laughter — a panting sound — when tickled. Recent research shows that even baby rats squeal with apparent pleasure when tickled, although you need an ultrasound detector to hear the sounds because they are at frequencies too high for human ears to detect. They are interpreted as sounds of joy because they differ markedly from distress calls, being similar to the sounds made by a male rat while courting a female. The possibility that tickling behaviour is widespread among mammals suggests that it may lie at the heart of the evolution of complex social behaviour.

Why then do we laugh when tickled? Laughing might not simply be a social expression of happiness. Some have suggested that the components of laughter — convulsion of the abdomen, production of sniggering noises, tears streaming from the eyes — all serve the general purpose of releasing tension in a social situation. Nervous laughter often occurs during tense situations, and there are striking similarities between laughing and crying hysterically. Being tickled certainly causes the body to become tense, through increased muscle tone.

An alternative view is that of Vilayanur Ramachandran of the University of California, San Diego, who claims that we laugh to tell other people that a potentially threatening situation is not serious. ‘You approach a child, hand stretched out menacingly … But no, your fingers make light, intermittent contact with her belly,’ he writes. As a result of being tickled the child laughs, as if to inform other children, ‘He doesn't mean harm. He's only playing.’ Some psychologists have suggested that the sense of humour evolves during individual development, starting with the baby's giggling in response to being tickled, later maturing into a tendency to laugh at unusual faces and situations, and finally maturing into an appreciation of jokes, subtle wit, and irony.

It all starts, though, with that first tickle. Without tickling, some suggest, there might be no humour at all.

Sarah-Jayne Blakemore

Bibliography

Darwin, C. (1872). The expressions of the emotions in man and animals. John Murray, London.
Ramachandran, V. S. (1998). Phantoms in the brain. Fourth Estate, London.

See also laughter and humour; pleasure.